A liquid chromatograph employs a liquid sample introduction device for selecting one from many liquid samples and introducing it into a column. FIG. 15 is a diagram schematically showing flow passages of a liquid sample introduction device in a conventional liquid chromatograph (Patent Literature 1).
As shown in FIG. 15, in a liquid sample introduction device 120 for a liquid chromatograph, two valves are used: a first passage switching valve 101 for switching a high-pressure mobile phase to be supplied to a column 104; and an normal-pressure second passage switching valve 102 for collecting sample liquid and washing a sampling needle 111. In order to connect a plurality of ports one another, both valves employ a rotary valve including a stator having openings corresponding to the respective ports and a rotor having communication passages to allow two of the openings of the stator to communicate with each other.
In the example of FIG. 15, the first passage switching valve 101 employs a rotary valve having six ports a′ to f′. Four of the ports are connected to a mobile phase liquid supply pump 103, the column 104 of the chromatograph, the sampling needle 111, and a sample injection unit 112, respectively, and two of the ports are connected to two ports of the second passage switching valve 102, respectively.
The second passage switching valve 102 employs a rotary valve having one common port g′ and five peripheral ports. The common port g′ and one peripheral port 1′ are connected to a measuring pump 113, and the other four peripheral ports to the two ports of the first passage switching valve 101, a cleaning liquid container 107 and a washing container 114.
In this liquid sample introduction device, a procedure for introducing a sample to the column 104 is as follows. First, the rotor of the first passage switching valve 101 is set at the position shown in FIG. 15 to connect the mobile phase liquid supply pump 103 and the column 104 to each other. Thereby, a mobile phase in a mobile phase container 105 is supplied to the column 104 at high pressure. In this state, the rotor of the second passage switching valve 102 is switched to the position shown in FIG. 15 and the sampling needle 111 is inserted into a sample liquid container 106 to suck a liquid sample of a predetermined amount with the measuring pump 113 and to retain it in a sampling loop 116. Next, the sampling needle 111 is inserted into the sample injection unit 112 and the rotor of the first passage switching valve 101 is rotated, and thereby, the liquid sample retained in the sampling loop 116 is pushed out into the sample injection unit 112 with the mobile phase liquid supply pump 103. Thereby, the liquid sample is injected into the mobile phase and sent to the column 104.
In the case where after injecting a first liquid sample as above, another (second) liquid sample is handled in the liquid sample introduction device 120, the first liquid sample attached to inside and outside of the sampling needle 111 must be prevented from contaminating the second liquid sample (contamination). Thus, the sampling needle 111 is inserted into the washing container 114 and the exterior of the sampling needle 111 is washed by, first, setting the rotor of the second passage switching valve 102 to the position indicated by the solid line in FIG. 16 to suck and retain cleaning liquid once in the measuring pump 113, and next, switching the rotor to the position indicated by the broken line to feed the cleaning liquid retained in the measuring pump 113 to the washing container 114. Moreover, the interior of the sampling needle 111 is washed by discharging the cleaning liquid from the measuring pump 113 with the passage being rotated counter clockwise by 60 degrees further from the position indicated by the broken line in FIG. 16. These steps are repeated as needed to sufficiently wash the interior and the exterior of the sampling needle 111.